Fix build with Meatpack only on 2nd port (#21336)

Co-authored-by: Scott Lahteine <github@thinkyhead.com>

Marlin/src/HAL/HAL.h

 
 #include HAL_PATH(.,HAL.h)
 
-#ifdef SERIAL_PORT_2
-  #define NUM_SERIAL 2
-#else
-  #define NUM_SERIAL 1
-#endif
-
 #define HAL_ADC_RANGE _BV(HAL_ADC_RESOLUTION)
 
 #ifndef I2C_ADDRESS

Marlin/src/feature/meatpack.cpp

 #if HAS_MEATPACK
 
 #include "meatpack.h"
-MeatPack meatpack;
 
 #define MeatPack_ProtocolVersion "PV01"
 //#define MP_DEBUG

Marlin/src/inc/Conditionals_LCD.h

   #define UNUSED_E(E) UNUSED(E)
 #endif
 
-#if ENABLED(DWIN_CREALITY_LCD)
-  #define SERIAL_CATCHALL 0
-  #ifndef LCD_SERIAL_PORT
-    #define LCD_SERIAL_PORT 3 // Creality 4.x board
-  #endif
-#endif
-
 /**
  * The BLTouch Probe emulates a servo probe
  * and uses "special" angles for its state.
   #define HAS_CLASSIC_E_JERK 1
 #endif
 
+//
+// Serial Port Info
+//
+#ifdef SERIAL_PORT_2
+  #define NUM_SERIAL 2
+  #define HAS_MULTI_SERIAL 1
+#elif defined(SERIAL_PORT)
+  #define NUM_SERIAL 1
+#else
+  #define NUM_SERIAL 0
+  #undef BAUD_RATE_GCODE
+#endif
 #if SERIAL_PORT == -1 || SERIAL_PORT_2 == -1
   #define HAS_USB_SERIAL 1
 #endif
   #define HAS_ETHERNET 1
 #endif
 
+#if ENABLED(DWIN_CREALITY_LCD)
+  #define SERIAL_CATCHALL 0
+  #ifndef LCD_SERIAL_PORT
+    #define LCD_SERIAL_PORT 3 // Creality 4.x board
+  #endif
+#endif
+
 // Fallback Stepper Driver types that don't depend on Configuration_adv.h
 #ifndef X_DRIVER_TYPE
   #define X_DRIVER_TYPE  A4988

Marlin/src/inc/Conditionals_adv.h

 #else
   #define HAS_USER_ITEM(N) 0
 #endif
+
+#if !HAS_MULTI_SERIAL
+  #undef MEATPACK_ON_SERIAL_PORT_2
+#endif
+#if EITHER(MEATPACK_ON_SERIAL_PORT_1, MEATPACK_ON_SERIAL_PORT_2)
+  #define HAS_MEATPACK 1
+#endif

Marlin/src/inc/Conditionals_post.h

 #if BUTTONS_EXIST(EN1, EN2, ENC)
   #define HAS_ROTARY_ENCODER 1
 #endif
-
-#if !NUM_SERIAL
-  #undef BAUD_RATE_GCODE
-#elif NUM_SERIAL > 1
-  #define HAS_MULTI_SERIAL 1
-#endif
-
-#if !HAS_MULTI_SERIAL
-  #undef MEATPACK_ON_SERIAL_PORT_2
-#endif
-#if EITHER(MEATPACK_ON_SERIAL_PORT_1, MEATPACK_ON_SERIAL_PORT_2)
-  #define HAS_MEATPACK 1
-#endif

buildroot/share/PlatformIO/scripts/common-dependencies.h

  * Used by common-dependencies.py
  */
 
-#define NUM_SERIAL 1 // Normally provided by HAL/HAL.h
-
 #include "../../../../Marlin/src/inc/MarlinConfig.h"
 
 //